The judge overseeing the custody case between Mel Gibson and Oksana Grigorieva has ordered an investigation into the leaking of sealed court documents.

Earlier this week, TMZ published Mel's sworn declaration in the custody battle with his former girlfriend, in which he reportedly admits "slapping" Oksana because he says she was "hysterical" and endangering their one-year-old child.

According to Oksana's lawyer Martin Garbus, the confidential documents were "stolen probably from court" and it's likely the person responsible "got paid a good deal of money".

As well as Mel's account, TMZ has also published sworn statements made by Oksana and another witness in court.